The injection molding process usually comprises preparing a polymeric material in an injection unit of an injection molding machine, injecting the now-molten material under pressure into a closed and clamped mold that is water cooled, solidifying the material in its molded shape, opening the mold and ejecting the part before beginning the next cycle. The polymeric material typically is supplied to the injection unit from a hopper in the form of pellets or powder. The injection unit transforms the solid polymeric material into a molten material, typically using a feed screw, which is then injected into a hot runner or other molding system under pressure from the feed screw or a plunger unit. A shut off valve assembly is typically provided to stop and start the flow of molten material from the barrel to the molding system.
Numerous types of valve assemblies can be used, including sliding piston valves and rotary valves. An example of a prior art sliding piston valve assembly for an injection unit can be found in U.S. Pat. No. 4,140,238 to Dawson (published Feb. 2, 1979). An example of a prior art rotary valve assembly for an injection unit can be found in U.S. Pat. No. 4,054,273 to Neuman (published Oct. 18, 1977).
Efforts have been made to improve the rotary valve assembly. European patent 0 494 304 B1, entitled “Rotary Valve of Injection Molding Machine” to YOKOTA, Akira et al. (published on Sep. 7, 1994) teaches a rotary valve assembly of an injection molding machine provided with a cylindrical valve chamber formed in the flow passage in which molten resin is filled under pressure and through which molten resin flows from the screw side to the nozzle side, wherein a cylindrical valve body having a through hole radially piercing through the body for ensuring unobstructed flow through the flow passage so that the through hole may agree with the axial line of the cylindrical valve chamber is fitted into the valve chamber slidably around the axial line and circumferential grooves are formed in the circumferential direction on both sides of the through hole and located along the axial line of the cylindrical valve body on the peripheral surface thereof so that even a small driving torque can actuate the cylindrical valve body.
Japanese patent 09132218A, entitled “Shutoff Nozzle for Injection Molding Machine” to MASATAKA et al (published on May 13, 1997) teaches: In an extrusion molding machine shut-off nozzle made capable of rotation between a position in which a molten resin passage is connected and a position in which the molten resin passage is cut off, and a housing is provided at some position along the nozzle having the molten resin passage whereby molten resin is fed to a metal mold from an extrusion molding machine, with rotary means provided at the end of a cylindrical rotary valve that has a through-hole in the interior of said housing and is freely rotatably inserted; a pressure reducing valve that temporarily admits molten resin left on a hot runner prior to commencement of suck-back is arranged in a direction intersecting the nozzle.